Hydrocracking is gaining in importance in refining as the need to convert heavy fractions into lighter fractions which can be upgraded as fuels increases. This results from the increasing demand for fuels. Such upgrading involves a relatively large reduction in the molecular weight of the heavy constituents which can, for example, be achieved through cracking reactions.
The catalytic hydrocracking process uses catalysts containing a hydrogenating, desulphurising and denitrogenating function provided by the active phase based on transition metals, and an acidic function, generally provided by the amorphous matrix or a zeolite, or a mixture thereof. A good hydrocracking catalyst will be constituted by a properly adjusted hydrogenating function and acidic function. Hydrocracking is used to treat feeds such as vacuum gas oils, and atmospheric or vacuum residues, which may or may not be deasphalted. Hydrocracking can produce highly purified lighter cuts, i.e., with a low sulphur, nitrogen and metals content.
Increasing the activity and selectivity of hydrocracking catalysts is thus important. One means consists of acidifying the matrix without poisoning the activity of either the transition-metal based hydrogenating phase or the cracking activity of the zeolite-based acidic phase.